DNS解析时，TCP 从哪个 IP 进来，就从哪个 IP 解析

chain.go

@@ -212,6 +212,13 @@ func (c *Chain) dialWithOptions(ctx context.Context, network, address string, op
 					IP: ip,
 				}
 			}
+		} else if inboundIP != nil && strings.ToLower(network) == "udp" {
+			ip := inboundIP.(net.IP)
+			if !ip.IsLoopback() && !ip.IsPrivate() {
+				d.LocalAddr = &net.UDPAddr{
+					IP: ip,
+				}
+			}
 		}
 		return d.DialContext(ctx, network, ipAddr)
 	}

dns.go

@@ -83,7 +83,11 @@ func (h *dnsHandler) Handle(conn net.Conn) {
 	if resolver == nil {
 		resolver = defaultResolver
 	}
-	reply, err := resolver.Exchange(context.Background(), b[:n])
+	ctx := context.Background()
+	if inboundAddr, ok := conn.LocalAddr().(*net.TCPAddr); ok {
+		ctx = context.WithValue(ctx, "InboundIP", inboundAddr.IP)
+	}
+	reply, err := resolver.Exchange(ctx, b[:n])
 	if err != nil {
 		log.Logf("[dns] %s - %s exchange: %v", conn.RemoteAddr(), conn.LocalAddr(), err)
 		return